The respiratory control center is composed of the dorsal respiratory group and the ventral respiratory group. Rhythmic breathing depends on a continuous (tonic) inspiratory drive from the dorsal respiratory group and on intermittent (phasic) expiratory input from the cerebrum, thalamus, cranial nerves, and ascending spinal cord sensory tracts. The peripheral and central chemoreceptors respond to changes in PaCO2 and pH. The peripheral chemoreceptors (carotid and aortic bodies) are the only chemoreceptors that respond to changes in PaO2.
Calverley PMA, Koulouris NG. Flow limitation and dynamic hyperinflation: key concepts in modern respiratory physiology. Eur Respir J. 2005;25:186-199.
Canning BJ. Afferent nerves regulating the cough reflex: mechanisms and mediators of cough in disease. Otolaryngol Clin N Am. 2010;43:15-25.
Leff AR, Schumacker PT. Respiratory Physiology: Basics and Applications. Philadelphia: WB Saunders; 1993. Nishino T. Dyspnoea underlying mechanisms and treatment. Br J Anaesth. 2011;106:463-474.
CO2responsiveness,havebeenimplicated.Placinginfantsontheirbackstosleep(whichreducesthepotentialforCO2rebreathing)hasdramaticallydecreased(butnoteliminated)therateofdeathfromthissyndrome.
3.
Acute hypoxia and chronic hypoxia affect breathing differently because the slow adjustments in CSF [H+] in chronic hypoxia alter sensitivity to CO2.
4.
Irritant receptors protect the lower respiratory tract from particles, chemical vapors, and physical factors, primarily by inducing cough. C fiber J receptors in the terminal respiratory units are stimulated by distortion of the alveolar walls (by lung congestion or edema).
5.
The two most important clinical abnormalities of breathing are obstructive and central sleep apnea.
6.
PaO2, PaCO2, and pH remain within normal limits during moderate exercise; however, during strenuous exercise, pH falls, which stimulates ventilation, whereas PaO2 and PaCO2 remain relatively normal.
Otis AB. A perspective of respiratory mechanics. J Appl Physiol. 1983;54:1183-1187.
Sheel AW, Romer LM. Ventilation and respiratory mechanics. Compr Physiol. 2012;2:1093-1142.
Wasserman K, Beaver WL, Whipp BI. Gas exchange theory and the lactic acidosis (anaerobic) threshold. Circulation. 1990;81(1 suppl):1114-1130.
Wine JJ. Parasympathetic control of airway submucosal glands: central reflexes and the airway intrinsic nervous system. Auton Neurosci. 2007;133:35-54.
Upon completion of this chapter, the student should be able to answer the following questions: 1.
Describe the components of the mucociliary clearance system and their role in the removal of xenobiotic substances and particulates.
2.
Explain how particle characteristics and properties influence their deposition and clearance.
3.
Compare and contrast the major mechanisms of particle deposition.
4.
Compare and contrast the mucosal and systemic immune responses.
5.
Describe unique features of immunoglobulin A and why it is well suited for the mucosal environment and protection.
6.
Compare and contrast adaptive and innate immune cells in the respiratory system.
7.
Describe the various metabolic processes in the lung.